1. Field
One embodiment of the invention relates to an information storage medium such as an optical disk and a method for reproducing and recording the storage medium.
2. Description of the Related Art
As a write-once type optical disk using an organic dye material for a recording layer, there has been commercially available a CD-R disk using a recording/reproducing laser light source wavelength of 780 nm and a DVD-R disk using a recording/reproducing laser light beam wavelength of 650 nm. There is proposed that a cyanine dye thin film capable of changing a physical property with a comparatively long wavelength, for example, with light having 790 nm is used for a recording layer (for example, refer to Jpn. Pat. Appln, KOKOKU Publication No. 6-43147).
On the other hand, in principle, density is increased in inverse proportion to a square of a recording/reproducing laser light source wavelength, and it is desirable that a shorter laser light source wavelength be used for recording/reproducing application. In recent years, a next-generation optical disk with high density has been developed. Here it is presumed that a recording or reproducing laser light source wavelength close to 405 nm (namely, in the range from 355 nm to 455 nm) is used. With respect to an organic dye recording material optimized with light of 650 nm, recording/reproducing characteristics significantly change if light to be used is shorter than 620 nm in wavelength. Thus, an organic dye material for 620 nm can be used as a recording later of a next-generation optical disk.